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Patients with β thalassemia have decreased β globin chain synthesis, which causes hypochromic, microcytic anemia (mean corpuscular volume <80 µm³).  Reduced β globin synthesis also results in the precipitation of unpaired α chains within red cells, causing membrane damage.  This subsequently leads to the death of red cell precursors in the bone marrow (ineffective erythropoiesis) and lysis of circulating erythrocytes (hemolysis).

Normal erythrocytes have an area of central pallor that typically measures 1/3 of the cell diameter.  Patients with β thalassemia classically have blood smears showing small red cells with an increased area of central pallor, as seen in the image above.  Other common findings include anisopoikilocytosis (variation in size and shape), target cells, nucleated red cell precursors, and basophilic stippling.

(Choices A and E)  Hyperchromia is characterized by reduced central pallor due to increased hemoglobin concentration and is usually associated with spherocytosis.  Hereditary spherocytosis is caused by a variety of molecular defects in the genes that encode certain red cell membrane proteins (eg, spectrin, ankyrin, band 3, protein 4.2).

(Choice B)  Iron deficiency often leads to hypochromic, microcytic anemia and is commonly caused by chronic, asymptomatic bleeding (eg, slow gastrointestinal bleed, abnormal menstruation).  In contrast, patients with thalassemia often have iron overload, not iron deficiency.

(Choice D)  Red blood cell sickling occurs in sickle cell anemia, which is caused by an A to T mutation in the β globin gene that results in glutamate being substituted with valine at position 6.

Educational objective:
β thalassemia results in hypochromic, microcytic anemia due to decreased β globin chain synthesis.  Unpaired α chains precipitate within red cells and cause membrane damage, leading to ineffective erythropoiesis and hemolysis.